The present invention relates generally to vehicle horn systems and, more particularly, vehicle horn systems used in conjunction with an airbag module.
Driver side airbag modules, which include an airbag cushion and an airbag module cover, are normally positioned within a hub of a steering wheel of an automobile. This happens to be the same area, which conventionally includes the horn switch. Accordingly, the airbag module cover must additionally serve to actuate the horn switch.
Horn switch designs have included a floating horn switch. Floating horn switches typically comprise a pair of conductive members, one of which is movable with respect to the other, and when in. a relaxed state, the movable member is biased away from the other. Applied pressure on the movable member pushes the conductive members together to close a circuit and actuate the horn. Pressure is applied to the horn switch by the airbag module cover in the hub of the steering wheel, which is depressed by the driver.
The introduction of the airbag module at the steering wheel hub complicated the design of the horn switch and the airbag module cover. For example, the cover should not require an unreasonable degree of depression or an unreasonable amount of applied pressure to actuate the horn switch, the horn switch should not be susceptible to inadvertent actuation, and the horn switch must not become unattached from the airbag module cover upon inflation of the airbag.
In some horn switch and airbag module cover configurations, the switch was compressed against the folded airbag cushion located behind the airbag module cover. These configurations required a large degree of airbag module cover depression and a large amount of force to activate the switch.
Other horn switch and airbag module cover configurations attempted to overcome these problems by securing the switch directly to the airbag module cover or tightly sandwiching the switch between the cover and an attached switch backing plate. However, these combinations made the switches susceptible to inadvertent actuation due to thermal contraction or expansion of the airbag module cover at extreme temperatures. In addition, the amount of pressure required to activate the horn switch also varied substantially as a function of ambient temperature, which affects the flexibility of the cover and backing plate.
Another type of inadvertent horn activation can occur from the vehicle operator releasing the steering wheel till to mechanism causing the steering rail to travel from either its lowest or highest tilt position to it""s complementary opposite position. This motion can cause a high g-force to be applied to the steering wheel due to it""s abrupt stopping. Such an abrupt stopping may cause a floating horn switch to close and open very quickly (commonly referred to as switch bounce), which turns the horn relay on. This is particularly true when the steering column is released from its lowermost position and is allowed to travel freely to it""s highest allow position.
In addition, switch bouncing and inadvertent horn activation may be caused by steering column vibrations that are encountered as the vehicle travels over a bumpy road.
Accordingly, it is desirable to provide an airbag module cover having a horn switch that does not require an unreasonable degree of cover depression or an unreasonable amount of applied pressure for actuation, and is not susceptible to inadvertent actuation resulting from g-forces related to the tilting of the steering wheel column and/or the vehicle traveling over a bumpy surface.
A horn activation system, which activates a switch for driving a horn, the horn activation system includes a discriminating device that discriminates between the forces being applied to the switch. The discrimination device connects the switch to a power supply for activating the horn when the force being applied to the switch is applied for a time period greater than a predetermined value.
In one embodiment, the switch is a floating horn switch and the predetermined value is sufficiently large enough to eliminate the majority of inadvertent horn activations due to switch bounce.
In another embodiment, the horn activation system is utilized with a steering system having an airbag module.
The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.